Numerous methods and devices are known for producing continuous bags of thin material, such as polyethylene. One well known example is the plastic bag commonly used in grocery stores or supermarkets. These bags are characterized by being in a continuous row on a reel with perforations through the bag separating one bag from the other. To use each bag, the shopper grasps a bag, tugs the bag thereby tearing it from the reel along a line of perforation which marks the end of one bag and the beginning of the adjacent bag on the reel. Thus, the line of perforation serves as the connection between one bag and another while on the reel as well as the opening of a bag once torn along the line perforation.
It is, however, desireable in certain applications to manufacture such continuous bag with each bag connected to the adjacent bag but having an opening along one side of the perforation. Such continuous bags are used in other manufacturing processes in which items are inserted into each bag through the opening in a continuous fashion. Thus, in such applications, it is desireable to manufacture continuous bags of thin material with each of the bags having an opening on a side.
Methods and apparati for the manufacture of continuous bags wherein each bag has an opening on a side are known. For example, my U.S. Pat. No. 4,500,307 entitled "Apparatus for Producing Continuous Bags of Thin Wall Material" (issued Feb. 19, 1985) discloses one such method and apparatus. In my previously patented invention, a length of continuous tubing is transformed to a length of continuous bags, each bag having an opening on a side and yet connected to one another by a line of perforation, is produced by twisting the tubing 90 degrees in one direction, passing the twisted tubing in a direction of production over a roller wherein one half of the roller has a cutting edge and the other half has a perforating blade, twisting the tubing 90 degrees in a direction opposite to the first twist to return it to its original orientation, and passing the tubing through a means for sealing the two layers of tubing together further down along the direction of production.
My previous invention had suffered from several disadvantages. Firstly, it did not conveniently allow for the adjustment of the length of the bags produced. The length of the bag product in that invention was a function solely of the size of the outer diameter of the cutting/perforating roller, which also functioned to advance the tubing along the direction of production. Bags produced from that method and device were roughly equal to the distance around the perimeter of the cutting/perforating roller. Thus, in order to change the length of the bag produced, it was necessary to use a different roller with a different outer diameter.
Secondly, the means for sealing the tubing to form the bottom end of bags is disposed a substantial distance away from the cutting/perforating roller along the direction of production. Thus, the tubing is perforated, advanced a distance and sealed. The sealing means seals the tubing to form the bottom of a bag by making physical contact with the tubing at a point adjacent to one of the lines of perforation/cut which had previously been made by the roller some distance before. Thus, the precision with which the perforating/cutting roller and the sealing means work together in synchronicity is an important factor in the successful operation of my prior device. Such synchronicity is difficult to achieve given the fact that the perforating/cutting roller and sealing means are separated by quite a distance.
There is, thus, a need for a method and apparatus for producing continuous bags having an opening on one side in which the length of the bags produced are easily adjusted. There is a further need for such a method and apparatus wherein the synchronicity necessary for the cooperation of the perforating, cutting and sealing steps is more easily attained.
The present invention addresses these needs and others.